3,354 research outputs found
Ablation of Martian glaciers
Glacier like landforms are observed in the fretted terrain of Mars in the latitude belts near + or - 42 deg. It was suggested that sublimation or accumulation-ablation rates could be estimated for these glaciers if their shapes were known. To this end, photoclinometric profiles were obtained of a number of these landforms. On the basis of analyses of these profiles, it was concluded that ice is chiefly ablating from these landforms that either are inactive rock-glaciers or have materials within them that are moving exceedingly slowly at this time. These conclusions are consistent with other geologic information. The analyses were performed using a two-dimensional model of an isothermal glacier
Global petrologic variations of the Moon: A ternary-diagram approach
A ternary-diagram approach is used to show on a single map as much detailed geochemical information concerning petrologic variations within the lunar crust as is possible. The classification map shows the global spatial distributions of end-member compositions, the transitional spatial relations between end-member compositions, and quantitative estimates of relative proportions of each end member at each pixel location within the orbital groundtracks. The use of elemental ratios in this analysis, instead of the commonly used elemental bivariate diagrams, shows geologic information that is otherwise hidden in individual elemental databases
A chemical and petrological model of the lunar crust
Information is given on the composition and structure of the lunar crust. A lunar model is illustrated, indicating that it has essentially two layers, anorthositic mixed rocks overlaying a generally noritic crystalline basement. Implications relative to lunar evolution are discussed
History and morphology of faulting in the Noctis Labyrinthus-Claritas Fossae Region of Mars
The topographically high areas cut by Noctis Labyrinthus, Noctis Fossae, and Claritas Fossae were subjected to only minor resurfacing during and following local tectonic activity. Principal resurfacing materials consist of lava flows from Syria Planum and Tharsis Montes. Thus, these areas preserve much of the fault record produced by tectonism in this region. Although recent geologic maps of the area have been produced from Viking images, the only detailed fault histories available until now were described from Mariner 9 images. Much of the faulting in the Tharsis tectonic province was centered in Syria Planum; therefore, understanding the fault history in this region is critical to understanding the stress history and tectonism of Tharsis as a whole
Theoretical Analysis of Transpiration Cooling of a Liquid Rocket Thrust Chamber Wall
Transpiration cooling is a process that could reduce the overall weight of the cooling system of an actively cooled thrust chamber wall of a liquid rocket engine by up to 50% when compared to other active cooling techniques, increasing the thrust to weight ratio of the rocket engine. In this thesis, mathematical models and computer codes were developed for simulating the flow of a coolant and the transport phenomena in a transpiration cooled thrust chamber wall of a liquid rocket engine by treating the coolant in two ways: as an incompressible fluid and as a compressible fluid in local thermal equilibrium with the porous structures that make up the thrust chamber wall. The programs were run with similar conditions and the results show that the incompressible flow model is a useful tool for accurately determining the temperature distribution inside the thrust chamber wall. The incompressible flow model was also used to perform parametric studies involving varying the thickness and porosity of the porous liner section of the wall. The results of these parametric studies show that varying the thickness and/or porosity of the porous liner can be utilized as a means for controlling the flow of the coolant inside the wall as well as its general function as a structural support for the thrust chamber wall
Static and Dynamic Properties of Type-II Composite Fermion Wigner Crystals
The Wigner crystal of composite fermions is a strongly correlated state of
complex emergent particles, and therefore its unambiguous detection would be of
significant importance. Recent observation of optical resonances in the
vicinity of filling factor {\nu} = 1/3 has been interpreted as evidence for a
pinned Wigner crystal of composite fermions [Zhu et al., Phys. Rev. Lett. 105,
126803 (2010)]. We evaluate in a microscopic theory the shear modulus and the
magnetophonon and magnetoplasmon dispersions of the composite fermion Wigner
crystal in the vicinity of filling factors 1/3, 2/5, and 3/7. We determine the
region of stability of the crystal phase, and also relate the frequency of its
pinning mode to that of the corresponding electron crystal near integer
fillings. These results are in good semiquantitative agreement with experiment,
and therefore support the identification of the optical resonance as the
pinning mode of the composite fermions Wigner crystal. Our calculations also
bring out certain puzzling features, such as a relatively small melting
temperature for the composite fermion Wigner crystal, and also suggest a higher
asymmetry between Wigner crystals of composite fermion particles and holes than
that observed experimentally.Comment: Composite Fermion Wigner Crystal; 14 pages, 9 figure
Characterization of a thermally imidized soluble polyimide film
A soluble aromatic poly(amic acid) film was converted to a soluble polyimide by staging at 25 deg intervals to 325 C and characterized at each interval by several analytical methods. The behavior observed was consistent with an interpretation that a reduction occurred in molecular weight of the poly(amic acid) during the initial stages of cure before the ultimate molecular weight was achieved as a polyimide. This interpretation was supported by the results of solution viscosity, gel permeation chromatography, low angle laser light scattering photometry and infrared spectroscopy analysis. The results serve to increase the fundamental understanding of how polyimides are thermally formed from poly(amic acids)
The creation and persistence of a misaligned gas disc in a simulated early-type galaxy
Massive early-type galaxies commonly have gas discs which are kinematically
misaligned with the stellar component. These discs feel a torque from the stars
and the angular momentum vectors are expected to align quickly. We present
results on the evolution of a misaligned gas disc in a cosmological simulation
of a massive early-type galaxy from the Feedback In Realistic Environments
project. This galaxy experiences a merger which, together with a strong
galactic wind, removes most of the original gas disc. The galaxy subsequently
reforms a gas disc through accretion of cold gas, but it is initially 120
degrees misaligned with the stellar rotation axis. This misalignment persists
for about 2 Gyr before the gas-star misalignment angle drops below 20 degrees.
The time it takes for the gaseous and stellar components to align is much
longer than previously thought, because the gas disc is accreting a significant
amount of mass for about 1.5 Gyr after the merger, during which the angular
momentum change induced by accreted gas dominates over that induced by stellar
torques. Once the gas accretion rate has decreased sufficiently, the gas disc
decouples from the surrounding halo gas and realigns with the stellar component
in about 6 dynamical times. During the late evolution of the misaligned gas
disc, the centre aligns faster than the outskirts, resulting in a warped disc.
We discuss the observational consequences of the long survival of our
misaligned gas disc and how our results can be used to calibrate merger rate
estimates from observed gas misalignments.Comment: 10 pages, 7 figures. Accepted for publication in MNRAS. Revised
version: minor changes. A movie of the evolution of the gas disc can be
viewed at http://astro.berkeley.edu/~freeke/misalign.htm
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